The invention relates to grinding wheels.
Grinding is a widely used precision machining process, accounting for over 20% of all machining processes in the manufacturing industry. Referring to FIG. 1, one type of grinding process employs a rapidly spinning grinding wheel 10 bonded with abrasive materials 12 (e.g., diamond abrasive particles in a resin, vitreous, or metallic bond). The wheel 10 grinds workpiece 14 moving slowly underneath the wheel 10.
Ceramic materials such as silicon nitride, silicon carbide, aluminum oxide, and zirconia are hard, low density materials with high wear resistance and the ability to withstand high temperatures. Grinding is often used to machine ceramic workpieces and workpieces made of other materials into their final shape. Costs associated with grinding include the cost of preparing a wheel (e.g., wheel truing and dressing).
Truing typically rounds a wheel by machining excess abrasive material off its periphery as the wheel rotates. Initially, a truing tool engages the rotating out-of-round wheel intermittently, removing material from protruding areas and progressively engaging more of the periphery as the wheel is rounded.
Dressing conditions the wheel surface topography to achieve a desirable grinding behavior. Typically, a bonded abrasive dressing stick is passed over the wheel periphery to expose the abrasive grains by eroding away binder and possibly removing and/or fracturing diamond grains. Re-dressing is periodically needed during grinding to recondition or resharpen a worn wheel surface. Severe and/or frequent dressing can result in excessive wheel consumption, whereas too gentle or insufficient dressing can result in a dull wheel. Dressing frequently can be time consuming and reduce the life of expensive abrasive materials. On the other hand, grinding with a dull wheel causes increased grinding forces which can lead to chatter vibration and damage to the workpiece.
For precision grinding operations, the wheel depth of cut may be comparable to or smaller than the wheel out-of-roundness. Therefore, wheel engagement with the workpiece can vary considerably during a single rotation. The wheel may even completely lose contact with the workpiece during part of each rotation. This unsteady behavior can have a deleterious effect on the wheel surface and the quality of the ground workpiece.
Material removal during grinding occurs when abrasive grains interact with the workpiece. This interaction generally involves both ductile flow and brittle fracture. As an abrasive grain engages the workpiece, initial cutting by ductile flow is followed by localized fracture if the grain depth of cut and the resulting force on the grain becomes sufficiently large. By analogy with indentation fracture mechanics, two principal types of cracks have been identified: lateral cracks which cause material removal and radial cracks which cause strength degradation. The implication of this observation is that strength degradation may be minimized by promoting ductile flow instead of fracture at the ground surface. For finish grinding operations, this would usually require extremely slow removal rates in order to achieve a small enough grain depth of cut and small enough force per grain. However, as a wheel is used and the abrasive material becomes duller, force levels increase, making it necessary to periodically re-dress the wheel. Periodic truing may also be necessary to restore the macroscopic shape of the wheel.
Typically, operators monitor the grinding and preparation processes to determine when the wheel is rounded and when the wheel needs to be dressed. Because of the practical difficulty in assessing the condition of a rapidly rotating wheel, operators typically manage wheel usage based on observation and experience. For example, an operator may periodically stop a grinding process to examine wheel characteristics (e.g., roundness and dullness) at intervals determined by the type of workpiece being ground.
Embedded force and acoustic emission sensors and on-wheel electronics enable an operator to continuously monitor wheel conditions using sophisticated real-time techniques without interrupting the grinding process. Processing electronics can be attached to the wheel using a modular adapter disk that enables operators to easily reuse, maintain, and modify the electronics.
In general, in one aspect, the invention features a grinding wheel system that includes a grinding wheel with at least one embedded sensor and an adapter disk containing electronics that processes signals produced by each embedded sensor. The adapter disk is constructed to attach to the grinding wheel and to connect to each sensor lead when attached. The electronics include a transmitter that transmits sensor information to a data processing platform. The data processing platform includes a processor, a receiver that receives sensor information transmitted by the electronics, and instructions that cause the processor to process the received sensor information.
Different embodiments can include one or more of the following features. The grinding wheel may include at least one force sensor which may be positioned near the grinding wheel periphery. The grinding wheel may include at least one acoustic emission sensor which may be positioned near the grinding wheel rim. The sensors may be piezoceramic sensors.
The electronics can include an analog to digital converter connected to a sensor and a digital signal processor fed by the analog to digital converter. The electronics can include a multiplexer connected to the embedded sensors.
The data processing platform instructions can compare sensor information collected from different sensors at substantially the same time and/or compare sensor information collected from a single sensor at different times. The instructions can cause the processor to process sensor information using at least one neuro-fuzzy network.
In another aspect, a grinding wheel system includes a grinding wheel with at least one piezoceramic sensor embedded near the wheel periphery for detecting wheel forces and at least three piezoceramic sensors positioned near the grinding wheel rim. An adapter disk containing electronics that processes signals produced by the sensors attaches to the grinding wheel and connects to each sensor lead. The electronics include a multiplexer fed by the sensor leads, an analog to digital converter fed by the multiplexer, a digital signal processor fed by the analog to digital converter, and a radio frequency transmitter fed by the digital signal processor. The data processing platform includes a processor, a radio frequency receiver that receives sensor information transmitted by the adapter disk electronics, and instructions that cause the processor to process the received sensor information.
In another aspect, an adapter disk that processes signals produced by at least one sensor embedded in a grinding wheel includes at least one lead for connecting to each embedded sensor and electronics for processing sensor signals.
In another aspect, a computer program, disposed on a computer readable medium, that analyzes data acquired via sensors embedded in a grinding wheel includes instructions that cause a processor to receive sensor data representing force sensed by each sensor and analyzing the received data.
The computer program may determine, for example, wheel dullness, grinding mode, roundness, and/or roughness. The computer program can implement at least one neuro-fuzzy network.
The invention provides several advantages. The grinding wheel system permits sophisticated real-time analysis of grinding wheel conditions. The positioning of the force and acoustic emission sensors prevents the sensors from producing responses to normal wheel events (e.g., vibrations routinely produced during grinding). By housing electronics in an adapter disk, operators can easily reuse, maintain, and modify the electronics. The system""s data processing capabilities provide a wide variety of information regarding wheel characteristics.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages-of the invention will be apparent from the following detailed description, and from the claims.